The present invention generally relates to nanomaterials. The invention particularly relates to thin-films comprising nanomaterials and processes for producing and treating such films.
Nanomaterials are the subject of significant research across a broad spectrum of industries. As used herein, the term “nanomaterials” refers to zero-dimensional (0D) materials with all dimensions being nanoscale (as nonlimiting examples, quantum dots, nanoparticles, dendrimers, nanocapsules, Fullerenes, nanoclusters, and nanodispersions), one-dimensional (1D) materials with two dimensions being nanoscale and the third dimension being greater than nanoscale (as nonlimiting examples, nanofibers, nanotubes, nanowires and nanorods), two-dimensional (2D) materials with one dimension (thickness) being nanoscale and other dimensions being greater than nanoscale (as nonlimiting examples, graphene and boron nitride (BN) nanosheets, thin-films, and nanomembranes), and three-dimensional (3D) materials in which nanoscale features (i.e., 0D, 1D, and/or 2D materials) are present but with all dimensions greater than nanoscale. “Nanoscale” is defined herein as dimensions of up to 100 nanometers, e.g., 0.1-100 nm.
For devices that emit light (e.g., displays, LEDs, etc.), absorb light (e.g., photovoltaics, solar modules, photochemical devices, solar chemical factories, etc.), or control the transmission of light (e.g., smart windows), a non-transparent film (or a feature formed therefrom, for example, an electrode) blocks light and thus reduces the energy converted or light transmitted. Consequently, transparent conducting films (TCF) and components formed therefrom (for example, transparent conductive electrodes (TCEs)) that have desirable optical-electrical (or optoelectronic) properties are critical components in applications of the types noted above, and in particular have been widely used in flat panel displays, touch screen technologies, as well as thin-film solar cells and LEDs. Low-cost and large-scale manufactured TCFs and TCEs (hereinafter, collectively referred to as TCFs) have drawn increasing attention.
Currently, various types of material compounds, and particularly transparent conductive oxides (TCO) with outstanding optoelectronic properties have been used or considered for TCFs. Indium tin oxide (ITO) is widely viewed as a standard compound for most applications requiring optoelectronic properties. TCFs formed of ITO generally have a sheet resistance of as low as about 10 ohms/sq and a light transmission of up to about 90% in the visible spectrum. Zinc oxide (ZnO) thin-films have drawn much attention recently due to significant advantages over other TCO films, including ITO. Such advantages include chemical stability in reducing environments, and availability to doping with a wide range of materials. Among extrinsic n-type dopant elements, aluminum (Al) is the most widely used dopant in ZnO thin-films (aluminum-doped ZnO, or AZO). Unfortunately, TCO films have typically required high vacuum deposition, which is accompanied by issues such as instrumental complexity, high cost, and limited scalability.
Graphene, which is a 2D atomic crystal of carbon, has in a very brief span of time become instrumental in realizing goals in various disciplines of materials science. Applications in plasmonics, optoelectronics, transparent electrodes, LEDs, DNA sequencing, and protein chemistry are just a few examples. Future potential applications of graphene include wearable electronics, THz applications, IR lasers and many more. Parallel to the rise and establishment of graphene as an important material that could change existing technologies, several other 2D materials are joining the race, for example, boron nitride (BN), molybdenum sulfide, molybdenum selenide, tungsten sulfide, tungsten selenide, and many others.
At the core of practical applications of these 2D materials, their ability to be integrated onto a variety of nanomaterials of different dimensionalities (e.g., various “nanostructures”) is very desirable. Wet transfer is a common technique used for transferring graphene or BN atomic sheets to surfaces of target nanomaterials, which includes spin-coating of a thin PMMA layer onto CVD-coated graphene on a copper foil, removing the copper foil by etching in an aqueous solution of iron chloride, using deionized water to transfer the PMMA-coated graphene to a target nanomaterial, and finally removing the PMMA coating. Wet transfer of graphene typically results in wrinkles, air-gaps and voids that can give rise to compromised physical contact between the graphene (or other 2D material) and target nanomaterials. Such lack of physical contact of graphene with functional nanomaterials degrades the out-of-plane electronic transport and chemical interactions therebetween, and thus hampers several possible opportunities and frontline applications of hybrid integrated nanosystems composed of functional nanomaterials and graphene or other 2D materials. For example, the interface between functional nanomaterials and graphene is very crucial for various nanomaterial systems, such as plasmonic materials, ferroelectric materials, magnetic materials, DNAs, proteins, cells as well as other bio-organisms and other functional nanomaterials.
There is an ongoing desire to incorporate nanomaterials-based thin-films into a variety of applications, including TCFs.